Internal combustion engine



AD011. c H, L; DOHERTY j y f INTERNAL counsus'rxonv NGINE Filed oet. 2e, 19,27

? his EN'TRoPY sufyvagduaL Patented Dec. -1l, 1934 y ,UNITED STATES PATENT OFFICE* Lessen m'rEaNAL coMUs'rroN ENGmE Henry L. Doherty, New York, N. Y., assigner to Doherty Research Company, New York, N. Y., a corporation o! Delaware Application oetober 26, 1927, serial No. 228,716 1 s. claims. (o1. 12s-s2) The present invention relates to internal comthe Ways by which the recuperator maybe made bustion engines and more particularly to engines a profitable part of internal combustion engine employing recuperators, the present application .apparatus is to cool the air strongly during com-l being a. continuation in part of my prior applipression and to take the compressed air to thev 5 cation Serial No. 97,164, filed March '25, 1926, recuperator Without heating it. Cooling the air 5 for Internal combustion' engine and method of during compression, either in the compressing operating same. chambers or intermediate such chambers, or

It has been recognized widely thatregenerator both, not only reduces the work of compression and recuperator cycles theoretically are very but increases the capacity of the air entering ecient. Many attempts have been made to the recuperator to absorb heat and thereby in- 10 realize some of the theoretical advantages of creases the useful work obtainable from a given these cycles in practise, but no internal comrecuperator. Both cooling the air during combustion engine employing either a recuperator pression and heating the air in the recuperator or regenerator is now on the market, or in fact increases the overall eiiiciency in that they dehas ever been placed on the market. The recrease the negative work done in compressing 15 generator inwhich the ingoing air flows through the air and reduce the waste heat' in the exthe same passages that have been heated by haust gases.y The second Way in which lthe the exhaust gases is fatally defective in that it recuperator may be made commercially availnecessarily adds a large volume to the compresable is that of compressing the air adiabatically sion space. of the combustion chamber. Addiaiterit has passed through the recuperator and 20 tions to the compression space not only deafterward expanding it through substantially a crease the theoretical efficiency of the engine, greater temperature range, the temperature at but reduce its output per pound. The recuperathe end of said expansion being nearly as low tor in which the air passing to the combustion as that at the beginning of said adiabatic comchamber ows through diierent passages from pression.' The reasons Why this step of ad- 25 those taken by the exhaust gases does not add abatic compression after recuperation enhances to the clearance of the engine, but it has neverthe value of the recuperator is that it markedly theless not been used in practise. The difiiculincreases the eniciency of the entire cycle. It

ties in obtaining an internal combustion recu- Will be understood. that the strong cooling of perator engine capable of competing with those the air during compressions prior to recupera- 30 of the ordinary Diesel and Otto types have been tion may be used in the same cycle with the great, although the causes of the dilculties adiabatic compression subsequent to recupera- A were obscure.y tion.

It has been found that a recuperator engine, After recuperation, the air must be conducted Diesel engines must satisfy a number of simuland used in burning the fuel in the combustion taneous conclitions.-v A chamber. The products of combustion must It has been recognized that a recuperator does then be expanded to produce power. The exnot add to the commercial value of the Diesel or pansion usually occurs in the combustion cham- 40 Otto type of engine in which the air for comber but this is not essential. Asabove intimated, 40 bustion is compressed'in the combustion chamit is necessary that the expansion chamber be ber. One of the conditions to be met by the of the low clearance type, not over one-third recuperator engine is therefore that the air for the clearance employed in Otto or Diesel engines combustion be compressed wholly or in part in being preferred in the recuperator engine asa chamber or chambers separate from the comsuming equal compression in the two cases. bustion chamber. This, however, involves addi# 'Ihe compression of the air in a chamber sepational iirst cost and upkeep. In order that therate from the combustion chamber fortunately recuperator shalljustify itself commercially, it permits the combustion chamber to -be made must return to fhe combustion chamber a suiiisubstantially without clearance space. More- Cently large percentage 0f the heat Units not over, in order that there be sufficient heat units 50 utilized by the engine to pay for the cost and in the exhaust and on which the recuperator upkeep and interest charges -on both itself and can operate to make the recuperator worth the Separate COmPIeSSog; means. In order to while, but without undue use of fuel in the comaeeOmDliSh this result, il? has been fOund that at bustion chamber,A the combustion chamber must A leastl one of two Ways must be used. One 0f be heat insulated. Experiment has shown, that 55 in order to compete commercially with Otto or to the combustion chamber Without cooling it 35' heat insulation in the cylinders of Otto and Diesel engines reduces the capacity to such an extent that, not only is there no commercial advantage, but that the over-all efficiency of the engine is decreased. This has been found to be the case as to Otto and Diesel engines in spite of the increase in the theoretical cycle efficiency caused by heat insulation. In the recuperator engine in which the air is compressed externally of the combustion chamber, however, expansion of the air in the recuperator can be. readily made use of to maintain the pressure on the piston during a part of the engine stroke and thereby becomes an advantage rather than the opposite. It is essential to use heat insulation on the inner face of the cylinder including ythe cylinder head or the head of the expansion chamber or chambers in the cylinder. If,the combustionoccurs in a chamber outside the expansion Y cylinder, the combustion chamber must also be heat insulated. It is greatly preferred also to use heat insulating material on that part of the surface of the piston exposed to the combustion.

Another factor essential to the successful use of the recuperator engines has been found to be that the recuperator be of. the counterflow ype. r

In engines of moderate sizes, moreover, an important practical consideration has been found to reside in the use of the chamber in one end of the cylinder for compression while the chamber in the other 'end of the cylinder is used for combustion. This arrangement permits an engine of moderate size to combine the high heat emciency of the recuperator design with a satisfactory output per pound of weight. It is desirable, however, that the full capacity of the cylinder be used for compressing purposes at the compression end of the cylinder; otherwise, the output of a given engine cylinder isf reducedconsiderably. In compound engines, this applies particularly to the low pressure cylinder.

It is the principal object of the present invention to provide a design for a recuperator engine which shall overcome defects of the prior recuperator engines and which shall comply with the requirements as set out above.

Further objects and advantages ofthe present invention will be apparent to those skilled in the art from the following description taken in connection "with the accompanying drawing, in which:-' f

Fig. 1 is an elevation partly diagrammatic in character of an engine according to the present invention, parts being shown in section and parts being broken away for purposes of illustration.

Fig. 2 is a temperature-entropy diagram illustrating a `preferred temperature-entropy cycle for the operation of thefengine illustrated in Fig. 1.

In the drawing, 10 is the main shaft of an engine, the engine having a combustion cylinder 12 and a low pressure expansion cylinder 14. Cylinder 12 is divided into a joint reaction or combustion and expansion chamber 16 and compression chamber 18 by the piston 20. As illustrated, cylinder 12 is of the low* clearance typefand has a heat insulating lining 1'7 on the 'curved walls and head of chamber 16, while piston 20 has a Vheat insulating covering 21 on its face toward chamber 16. Cylinder 14 is divided into an expansion chamber 22 and a compression chamber 24, by the piston 26. Cylinder 14 and piston 26 also have heat insulating covering and lining 23 and 27 respectively. Low

pressure air, either from the atmosphere or from a super-charger is taken into chamber 24 through a valve 28 and receives a first stage of pistoned compression in this chamber. Air undergoing compression in chamber 24 preferably is cooled strongly, isothermal compression being desirable in many cases. A water spray lintroduced into chamber 24 at 30 and coming from pump 32 is a suitable cooling means for this purpose. As piston 26 approaches the crank end of the cylinder 14, the air is forced out of chamber 24 through valve 34. In the apparatus as illustrated, the air then enters an intercooler 36 `which may consist of a pipe coil over which water is led from the source 38. The air from inter-cooler 36 passes into the compression space 18 of the cylinder 12. It is preferred, however, that a trap 40 be connected in, the air line between chamber 24 and chamber 18 to remove water and moisture from the air. Air enters chamber 18 through an inlet valve 42. In the chamber 18 the air undergoes a second stage of pistoned compression and is preferably fur ther cooled strongly during this stage of cornpression by a water spray introduced into cyl-v inder 12 at 44, or by other suitable means. It will be observed that both cylinders 14 and 12 are Water jacketed as' indicated at 46, 46 throughout.`

the portions of the cylinders in contact with the piston rings of the pistons 20 and 26. The air compressed in chamber 18 is discharged there:

from through valve 48 into pipe 50. Pipe 50 preferably contains a trap 52 to remove water and moisture from the air. The pipe delivers air to the heating coils 54, 54 of the recuperator 56 in which `the air is heated by exhaust gases. at the time it enters coils 54 is converted into steam while passing through coils 54 of the recuperator. Air leaving recuperator or heating coils 54 enters the pipe 58 and is thereupon'- conducted to a compressor cylinder 60. Preferably the cylinder 60 is double acting as shown and in it the air is given a nal stage of compression. 'I'he compression in cylinder 60 is adiabatic, vthe compression spaces of cylinder 60 having heat insulation linings 61, 61 and the piston working in cylinder 60 has insulating extensions 63, 63, linings 61 and extensions 63 causing the compression in cylinder 60 tor-be adiabatic. Unless the compression of the air at the point in the cycle between the recuperator 56 and the combustion'chamber 16 is carried out in heat insulated chambers such'as those illustrated as used in compressor cylinder 60, the loss of heat is very great. The temperatu're and pressure of the airwhen entering cylinder 60 are both so high that a water' cooled compression chamber in cylinder 60 would act almost as an isothermal compressor. Air leaving cylinder 60 enters a receiver 62 and passes thence through pipe 64 to an intake valve 66. Air passes through the valve 66 into reaction or combustion chamber 16. The connections between cylinder 60and chamber 16 are insulated to prevent loss of heat and pressure. Due to heating in the recuperator 56 and during the adiabatic compression in cylinder 60 airA enters.

chamber 16 at a (temperature insuring the ignition of the fuel used without assistance from 21 which become highly heated on their exposedV Any moisture or water in the air:

chamber 22 the exhaust gases are discharged through the valve 74 into a conduit 76'by which they are carried into the casing of the recuperator 56. In the recuperator 56 the exhaust gases pass counterflow to the air passing through the coils 54. The exhaust gases are nally discharge from the recuperator 56 at a temperature very little higher thanthat of the airat the point at which the compressed air enters the recuper- `ator. The exhaust gases are discharged from the recuperator at point 78.

The valves for controlling the flow of air into and out of the combustion chamber 16 and the expansion chamber 22 are mechanically operated. As illustrated, these valves are operated from the cam shaft 80, shaft being driven in turn by a shaft 82 geared to the shaft 10. Cam mechanisms for operating valves of internal combustion engines are well known and any one of a variety of types may be employed in engines according to the present invention. The mechanism for operating valves 66, 70 and 74 vwill accordingly not bedescribed in detail. As illustrated, the valves controlling the ow of air into and out of chambers 24, and 18 and cylinders 60 are automatic in operation, being held normally closed by means of springs and opened when the pressure in the direction away from their seats overcomes the spring pressure. I do not limit myself however to the use `of automatic valves in the compression of the air.

The means for forcing liquid fuel at suitable pressure into the fuel pipe 68 and the means for governing the engine to prevent undue Variations of speed with variations of load, both are not illustrated herein. Means for supplying fuel to engines and for controlling the speed are both well known in the art and any suitable mechanism for such purposes may be employed in connection with the `present invention. These mechanisms therefore are not illustrated herein. The combustion chamber 16 of cylinder 12 is provided on the inner face of its side walls and on the inner face of its head with a heat insulating lining 17. Similarly the piston 20 is provided with an extension on the face toward the chamber 16 and said extension is provided with a heat insulating covering 21. The 17, andcovering 21. not only prevent the loss of heat from the engine cycle and thereby increase the eiiiciency of the engine butassist in igniting the fuel. The lining 17 and covering 21 are preferably of bonded Zircon. Suitable methods of bonding Zircon are known and include bonding it by small amounts of phosphoric acid, of precipitated iron or zirconium hydroxide,

form no part of the present invention, however, and are not claimed herein.

Preferably also the expansion chamber 22 in cylinder 14 is supplied with an insulating lining 23 and thepiston 26 has a corresponding extension provided with an insulating cover 27.

It will be seen that the engine disclosed herein contains the `elements disclosed in a prior application Ser. No. 97,164 by Henry L. Doherty, filed March 25, 1926. The engine according to the present application, however, as compared to said prior application, includes means for giving the air an additional stage of compression prior to the use of the air in the combustion chamber and more particularly an adiabatic compression stage intermediate the step of recuperation and that of combustion. The purpose of a stage of adiabatic compression after recuperation is more fully explained hereinbelow in connection with the cycle whose temperature entropy diagram is illustrated herein in Fig. 2 and which is disclosed also in said application, Ser. No. 97,164. `v

In the operation of the engine previously described, the air is cooled strongly 'during compression and prior to its passage through the recuperator. It is preferred that the cooling ofthe air prior to the recuperation be as nearly isothermal as practicable. In the temperatureentropy diagram illustrated in Fig. 2, the strongly cooled compression of the air as just mentioned is indicated by an isothermal line be ginning at point 84 and running to the point 86. After the strongly cooled compression the air enters the recuperator. and passes therethrough with resulting increase in both its temperature vand entropy as indicated in the curve running from point 86 to point 88. After passing through the recuperator, the air receives an adiabatic compression as indicated by the isentropic line extending from point 88 to point 90. After the adiabatic compression, the -air is burned with fuel with consequent rapid increase in temperature and some increase in entropy as indicated by the curve extending from point 90 in Fig. 2 to point 92. At point 92 in the diagram the temperature has reached a zone in which the dissociation of products of combustion is approached, and further combustion occurs substantially at this temperature as indicated by a line almost parallel tothe entropy axis and extending on the diagram from point 92 to point 94. 'I'he fuel having been completely consumed, adiabatic expansion thereupon takes place as indicated by the isentropic line,extending from point 94 to point 96. It is clear from'the diagram of Fig. 2 that the adiabatic expansionof the products of combustion passes substantially through the same temperature range as the diabatic compression which occurred in the cycle just subsequent to the recuperative heating of air and which is indicated on the diagram by the line -88-90.` In other Words, gases at point 96 of Fig. 2 are substantially at the same temperature as at point 88. After adiabatic expansion, the products of combustion pass through the recuperator and undergo changes of temperature and entropy as indicated by the line 96--84, thus closing the cycle. As to the cycle illustrated in Fig. 2, particular emphasis is laid upon -the adiabatic compression intermediate f nearly approach the ideal Carnot cycle.

Owing to the v general limitation which is placed'upon the temperatures attained during combustion by dissociation, the attainment of the objects enumerated is attended by an accentuation of the approach to isothermal, which is usually present. to some extent in commercial engines, as against adiabatic expansion.

As isalso well known, the eiciency of an en= gine is, measured by the average temperature of the net heat addition divided into the difference between the average temperature of the net addition and the average temperature of the net heat abstraction. Adiabatic compression at the point inthe cycle intermediate recuperation and combustion increes the thermal eiiciency in that it makes the air temperature at the beginning of combustion as high as possible and. thereby increases the average temperature of heat addition which occurs during the cycle, I'he adiabatic compression after recuperation increases thepower capacity of the engine by increasing the mean eiective pressure actingduring the power stroke. Furthermore, the adiabatic compression at the point of the cycle under consideration renders the sides of the temperature entropy diagram more nearly parallel. It is a. principle which has been recognizedl that any cycle in whose temperature-entropy diagram the lines representing the temperature increases are parallel to lines representing temperature decreases may be transformed into an equivalent Carnot cycle. Since the Carnot cycle is the theoretical cycle having maximum efficiency, it is clearl from the diagram of Fig. 2 that the step of adiabatic compression of air intermedi-`- ate the recuperation and the combustion as represented by a line parallelto the subsequent adiabatic expansion, adds to the eiciency of the cycle for this reason also. However, in order to take full advantage in engines of the opportunities aiforded by the adiabatic compression of air after recuperation, it has been found that it lis necessary that the subsequent adiabatic expansion of products of combustion should be carriedV to a point such that the temperature at the end of the adiabatic expansion is approximately equal to that at ,which the adiabatic compression of air began. In other words, the adiabatic expansion should preferably extend through substantially the same temperature range as thatof the adiabatic compression, as illustrated in Fig. 2. It has .been found that when adiabatic compression after recuperation is coupled with adiabatic expansion after combustion through substantially the same temperature as the compression, the cycle eiilciency is so high that theA cooling of the air in the compression before recuperationmay sometimes beomitted and still obtain a commercial. engine for certain purposes.

It will be observed that the entropy range between any twov points of equal temperature on the. recuperation curves 86-88 and 96-84 respectively, is the same as the entropy range caused by the combustion of the fuel. It has been found by comparing numerous diagrams that theV equality of entropy ranges just mentioned produces a cycle which, other things being equal, has a maximum efficiency. 'I'his broad principle, however, is claimed in said prior application Serial No. 97,164 and is claimed herein only in connection withV a cycle having an adiabatic compression step following recuperation.

The present invention has been described above in connection with a specific apparatus. It will be understood that I do not limit myself to details of construction, arrangement or operation as set out above except insofar as such details are plainly included in the following claims, it being intended to claim the invention as broadly as permitted by the prior art.

' Having thus described my invention, I claim:

'1. In an internal combustion engine, the combination of a combustion chamber having a heat insulating lining, a counter now recuperator connected to receive hot gases from said combustion chamber, means for cooling air compressed in said compression chamber and yfor delivering cool compressed air to said recuperator, a second compression chamber, means'for delivering hot compressed air from said recuperator to said second compression chamber, means for compressing the air further in said second compression chamber and at substantiaily constant entropy, and connections for delivering air from said second compression chamber to said combustion chamber at sub.- stantially the same temperaturqand pressure at which it leaves said second compression chamber.

2. lIn an internal combustion engine, the combination of means for compressing air, a recuperator, connections for passing air from said compressing means through said recuperator and counter ow to hot gases of combus# tion, means whereby-air which has passed through said recuperator is given asecond and adiabatic stage of compression, a low clearance combustion chamber, means for conducting air from said second compression means to said combustion chamber and for burning fuel therewith in said combustion chamber, means whre by the products of combustion are expanded` adiabatically under insulated conditions and to a temperature approximately equal to that of the air at the beginning of said adiabatic coinpression, and connections whereby the expanded products of combustion are conducted to said recuperator. f

3.,In an internal combustion engine, vmeans for compressing and for cooling air, a recuperator, means whereby cooled compressed air from.

products of combustion formed in said com bustion chamber are expanded adiabatically and to altemperature approximately equal to that of the air at the beginning of said adiabatic compression, and connections whereby productsA of. combustion are passed through ,said recuperator.

4. In an internal combustion engine, means for compressing air, a recuperator, means whereby air from said compressing means isV heated in said recuperator by passing counter' current to products of combustion, means for'v compressing adiabaticaly air which has been.

heated in said recuperator, a low clearance heat -insulated combustion chamber, means for combining air which has been compressed in said second compressing means with fuel in said combustion chamber and means whereby products of combustion are expanded and passe through said recuperator.

5. In an internal combustion engine, means for compressing air, a recuperator, means for heating the air from said means by passing it through said recuperator counter-flow to products of combustion, means for giving air from said recuperator a second and adiabatic stage of compression; a low clearance heatI insulated combustion chamber, means for combining vair from said second compressing means with fuel in said combustion chamber', means whereby products of combustion are expanded adiabatically under heat insulating conditions, to a temperature approximately equal to the temperature of the air at the beginning of said second stage of compression, and connections for leading expanded products of vcombustion to said recuperator.

6. In an internal combustion engine, neans for compressing air and for cooling it, a recuperator, meansv for heating air from; said means while passing through said recuperator counter-current to products of combustion, means for compressing air from said recuperator in a second and adiabatic stage of compression, a low clearance heat insulated combustion chamber, means for combining air with fuel in said combustion chamber, means whereby products of combustion from said chamber are expanded adiabatically while heat insulated, and connections whereby products of combustion-pass to said recuperator.

HENRY L. DOHERTY. 

